Various methods of hair removal are known. For example, the hair can be shaved from the body or can be removed by the use of tweezers or other instruments which pluck the hairs from the skin, such as devices including bent rotating coil springs and the like. In addition, chemical depilatory preparations and waxes have been formulated for the purpose of hair removal. Conventional depilatory preparations, often containing sulphide chemicals, act by weakening the structure of the hair to such an extent that scraping the cream off the skin breaks the hair at skin level and thus removes it. Alternatively, waxes can be applied to the skin which can then be peeled away with the hairs embedded therein.
Each of these methods has attendant disadvantages. Shaving brings only temporary alleviation since the roots of the hair are still present and the hair will grow again after a very short period. Also, there is the danger of cutting the skin on shaving. Chemical depilatory preparations tend to have an unpleasant smell and the use of waxes and coil spring devices can cause some discomfort.
Currently, waxes are increasing in popularity. Epilatory waxes tend to be supplied as generally solid materials which are melted prior to use. The molten material is applied to the skin, where at it cools and is then peeled away together with the unwanted hair. Often, a tool such as a spatula or stirrer is provided with the wax composition for applying the composition to the skin. Wax compositions may conveniently be heated in the container in which they are supplied, for example by means of a conventional or microwave oven or a hot water bath (a so-called "bain-marie"). However, a particular problem with such wax compositions lies in ensuring that the wax is heated to the correct temperature for application to the skin. If the wax is insufficiently hot, it may not be entirely molten and its effectiveness may be reduced. More seriously, if the wax is too hot, it may cause burns to the skin.
Therefore, it would be desirable to provide a means of ensuring that the wax is at the correct temperature before application to the skin.
Since the advent of thermochromic materials, indicator strips containing thermochromic materials have been applied to the outside of containers for temperature indication. For example, thermochromic liquid crystal inks have been used in labels placed on the outer surface of a container. However, the change in color of the ink of the label may not most accurately reflect the actual temperature of the contents of the container. For example, if the container is intended to be heated in a water bath, the label on the container would change as a consequence of the temperature of the water, and not the temperature of the contents of the container. Furthermore, thermochromic liquid crystal compositions change color at a precise temperature. Thus, an ink could be selected which would change color at a substantially precise temperature, for example at 50.degree. C. or at 60.degree. C.
However, such prior art systems are not ideal for use on a container of wax to indicate whether the wax is at a suitable temperature for application to the skin. This is because wax can be used safely and effectively over a reasonably broad temperature range, for example between about 44.degree. C. and 58.degree. C. Therefore, it would be preferable to be able to determine whether the temperature of the wax falls within a predetermined broad temperature range, rather than to be able to determine that the wax is at one specific temperature.